A Grand Prediction: Communicating and Evaluating 2018 Summertime Upper Blue Nile Rainfall and Streamflow Forecasts in Preparation for Ethiopia's New Dam

Annalise G Blum,Temesgen Alemneh,Ben Zaitchik,Sarah Alexander,Shraddhanand Shukla,Paul Block,Ying Zhang,Shu Wu

doi:10.3389/frwa.2019.00003

Abstract

When complete, the Grand Ethiopian Renaissance Dam (GERD) will be the largest hydropower dam in Africa. The GERD has become a focal point of geopolitical tensions because it will allow Ethiopia greater control over the Blue Nile River, Egypt’s main source of freshwater. To inform discussions of filling plans and responses, we created a probabilistic seasonal forecast for Upper Blue Nile rainfall and streamflow in the GERD basin. Eight statistical models and eight dynamical models were used to forecast the rainy season (June-September), which were then converted into river flow for June-December 2018. Both statistical and dynamical models predicted a high probability of average to above average rainfall as well as Upper Blue Nile flow in the GERD basin. Actual summer precipitation in 2018 was slightly below the long-term mean but well within the range considered to be “near normal.” Leveraging the increasingly online media landscape for science communication, we made the forecast publicly available through a blog and shared with regional decision-makers in advance of the 2018 rainy season. The blog attracted news coverage in the region focusing primarily on the relatively low likelihood of below-average Nile flow across the forecast ensemble. When asked for feedback on the blog, Ethiopian decision-makers and forecasters reported that flow predictions included in our blog were useful and not part of existing products. Access and comprehension were noted barriers to the use of these types of forecasts, consistent with prior research in forecast communication and dissemination. Forecasts available on such blogs can inform a shared understanding among decision-makers in the management of transboundary waters, yet effective communication and dissemination remain a challenge.

Highlights

Soon to be the largest hydropower dam in Africa, the controversial Grand Ethiopian Renaissance Dam (GERD) will allow Ethiopia greater control over the Blue Nile River, Egypt’s main source of freshwater
With GERD reservoir filling initially expected to begin during the summer of 2018, we developed a seasonal forecast for Upper Blue Nile rainfall and streamflow at the GERD and made the forecast publicly available on a blog in May 2018
Model hindcasts indicate that the statistical approaches had moderate skill due to some unexplained variance, and that skillful predictions could be obtained using a number of different model structures and predictor sets (Table 3 and Figure 3)

Summary

Introduction

Soon to be the largest hydropower dam in Africa, the controversial Grand Ethiopian Renaissance Dam (GERD) will allow Ethiopia greater control over the Blue Nile River, Egypt’s main source of freshwater. Ethiopia formally announced its intentions to construct the GERD in 2011, and, since that time, many studies have examined the potential impacts of the project on Ethiopia, on downstream riparians Sudan and Egypt, and on the East African power grid (Chen and Swain, 2014; Mulat and Moges, 2014; Satti et al, 2015; Tawfik, 2016; Wheeler et al, 2016). Ethiopia must fill the 74 cubic kilometer reservoir behind the GERD, which will impact downstream countries including Sudan and Egypt (King and Block, 2014; Zhang et al, 2016). If the filling of the reservoir occurs during years without much rain, Nile flows could be substantially reduced. This possibility has fueled speculation about the potential for a “water war” in the region (BBC, 2018). There have been calls for an agreement among affected countries to be made before filling of the GERD begins (Zhang et al, 2016)

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